1. Field of the Invention
The present invention relates to an apparatus for loading a substrate of a liquid crystal display (LCD) and, more particularly, to an apparatus for loading a substrate of an LCD capable of reducing the cost while enhancing the speed of a loading process of substrates into processing lines.
2. Discussion of the Related Art
Recently, as various mobile electronic devices, such as mobile phones, PDAs, and notebook computers are developed, demands for flat panel display devices, which are light, small, and thin are increasing for mobile electronic devices. Examples of flat panel display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs) which are being actively studied. Among them, the LCD is receiving much attention because of advantages including easy mass-production, simple driving unit, and high quality pictures. An LCD displays information on a screen using anisotropic properties of liquid crystals.
With reference to FIG. 1, LCD 1 includes a lower substrate 5, an upper substrate 3 and a liquid crystal layer 7 formed between the lower substrate 5 and the upper substrate 3. The lower substrate 5 is a driving element array substrate. Although not shown, a plurality of pixels are formed on the lower substrate 5. Each pixel on the lower substrate 5 includes a driving element such as a thin film transistor (TFT). The upper substrate 3 is a color filter substrate which includes color filter layers for actually implementing colors. Pixel electrodes and common electrodes are formed on the lower and upper substrates 5 and 3 (not shown), and an alignment film for aligning liquid crystal molecules of the liquid crystal layer 7 is coated (not shown). The lower and upper substrate 5 and 3 are attached by a sealant 9 with the liquid crystal layer 7 being formed therebetween. The amount of light transmitted through the liquid crystal layer 7 is controlled by driving the liquid crystal molecules, thereby allowing information to be displayed. The liquid crystal molecules are driven by a driving element formed on the lower substrate 5.
The fabrication process of the LCD includes a plurality of steps which will now be described with reference to FIG. 2. FIG. 2 shows two branches of processes. In FIG. 2, the left branch corresponds to the process for the lower substrate 5, and the right branch corresponds to the process for the upper substrate 3. First, in step S101, a plurality of gate lines and a plurality of data lines are formed to define each pixel region on the lower substrate 5 in the driving element array process. Further, in step S101, TFTs and driving elements are formed in the pixel regions, connected to the gate lines and data lines. In addition, pixel electrodes are formed connected to the TFTs through the TFT array process S101 to drive the liquid crystal layer when a signal is applied through the TFTs. At the same time, in step S104, R, G and B color filters for implementing colors and common electrodes are formed on the upper substrate 3 according to the color filter process S104.
Subsequently, in step S102, an alignment film is coated on the lower substrate 5 and then rubbed to provide an alignment anchoring force or a surface fixing force. At the same time, in step S105, an alignment film is coated on the upper substrate 3 and then rubbed to provide an alignment anchoring force or a surface fixing force. These forces are applied to the liquid crystal molecules of the liquid crystal layer formed between the upper and lower substrates 3 and 5.
Thereafter, in step S103, spacers for uniformly maintaining a cell gap spread on the lower substrate 5 is dispersed. And at the same time, in step S106, the sealant 9 is coated on an outer edge portion of the upper substrate 3. Subsequently, the lower and upper substrates 5 and 3 are attached by applying pressure thereto, in the assembling step S107.
The lower and upper substrates 5 and 3 are formed as large-scale glass substrates. In other words, a plurality of panel regions are formed on a single large-scale glass substrate, where the TFTs, the driving elements, and the color filter layers are formed on each panel region. Therefore, in order to fabricate each liquid crystal panel, the glass substrates should be cut and processed. This is performed in the cutting panel step S108.
Thereafter, in step S109, liquid crystal is injected into each of the processed liquid crystal panels through a liquid crystal injection hole, and the liquid crystal injection hole is sealed to form the liquid crystal layer. Finally, each liquid crystal panel is tested in the testing step S110.
Each process presented above is performed in separate processing equipment. Thus, whenever each process is completed, the substrates 3 and 5 are transferred to the next processing equipment. Here, the substrates 3 and 5 are transferred in the form of cassettes. The substrates 3 and 5 are initially loaded in a cassette, transferred while in the cassette to a different port, unloaded from the cassette, loaded to a corresponding processing equipment, and then subjected to a corresponding process.
FIG. 3 shows a related art substrate loading apparatus 70 for unloading the substrate 1 from the cassette 20 and loading it to the processing equipment 60. As shown in FIG. 3, the cassette 20 that receives a plurality of substrates 1 is positioned at port 30. In this case, the cassette 20 is arranged such that it can be either lifted or lowered in the port 30. As the substrate 1 is unloaded, starting from the lowermost substrate 1, the cassette 20 is lowered accordingly. A robot 50 is installed in front of the cassette 20. The robot 50 includes a base 51, robot arm 52, and a shaft 54. The base 51 is formed on a guide rail 40, which can move along the guide rail 40. The shaft 54, which is able to be rotated simultaneously when lifted, is installed on the base 51. The robot arm 52, which can extend to allow the substrate 1 to be mounted on an end portion thereof, is installed at the shaft 54. A processing equipment 60 is provided at the opposite side of the port 30 along the guide rail 40, and performs a process on the substrate 1 when the substrate 1 is unloaded from the cassette 20.
In the substrate loading apparatus 70 shown in FIG. 3, the arm 52 of the robot 50 is positioned with a pre-set height so as to be able to extend into the cassette 20 to mount the lowermost substrate 1. When the lowermost substrate 1 is unloaded and mounted on the robot arm 52, the robot 50 then moves along the guide rail 40 to load the unloaded substrate 1 into the processing equipment 60. After one substrate 1 is unloaded, the cassette 20 is lowered. Here, the movement distance of the cassette 20 is the same as the receiving interval inside the cassette 20, so that the next lowermost substrate 1 would be positioned at the height of the robot arm 52 (X2). Thereafter, the same process, previously mentioned, is repeatedly performed to load the next substrate 1 into the processing equipment 60. Such operation is repeatedly performed until all the substrates 1 received in the cassette 20 are unloaded. In other words, the operation is repeatedly performed until the uppermost substrate 1 in the cassette 20 is unloaded.
When the uppermost substrate 1 received in the cassette 20 is unloaded, the cassette 20 comes to a completely lowered state, where the cassette 20 contacts the bottom of the port 30. In this state, the uppermost substrate 1 is mounted on the robot arm 52. Thus, if the position (X2) of the robot arm 52 is not as high as distance from the bottom to the uppermost substrate 1 of the cassette 20 (X1), even after the cassette 20 is completely lowered, the uppermost substrate 1 of the cassette 20 cannot be mounted on the robot arm 52, making it impossible to unload the substrate 1. In other words, the height (X2) of the robot arm 52 should be greater than the height (X1) from the bottom to the uppermost substrate 1 of the cassette 20 (namely, X2≧X1) in order to unload the substrates 1 from the cassette 20. The height (X3) of the entrance 62 of the processing equipment 60 is generally lower than the height (X2) of the robot arm 52 (X2>X3). Thus, in order to load the substrate 1 unloaded from the cassette 20 into the processing equipment 60, the robot arm 52 should be lowered by a distance of X2−X3.
Therefore, in the related art substrate loading apparatus 70, the loading process is delayed since the robot arm 52 is repeatedly lifted up and lowered down to unload the substrates 1 from the cassette 20 and further to reload the substrates 1 into the processing equipment 60. In addition, as the height of the cassette 20 increases, which allows more substrates 1 to be received at the port 30 in a single cassette 20, the resulting distance that the robot arm 52 is to be lifted or lowered is further increased, which cause more delay in the loading process.